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MWSA's physical habitat approach - combining knowledge of habitat requirements with mechanisms of geomorphic and anthropogenic influence on stream channel form
Citation:
KAUFMANN, P. R. MWSA's physical habitat approach - combining knowledge of habitat requirements with mechanisms of geomorphic and anthropogenic influence on stream channel form. Presented at Seventh National Monitoring Conference, Denver, CO, April 25 - 29, 2010.
Impact/Purpose:
Effective environmental policy decisions benefit from stream habitat information that is accurate, precise, and relevant. The recent National Wadeable Streams Assessment (NWSA) carried out by the U.S. EPA required physical habitat information sufficiently comprehensive to facilitate interpreting biotic data, and to address habitat concerns in their own right.
Description:
Effective environmental policy decisions benefit from stream habitat information that is accurate, precise, and relevant. The recent National Wadeable Streams Assessment (NWSA) carried out by the U.S. EPA required physical habitat information sufficiently comprehensive to facilitate interpreting biotic data, and to address habitat concerns in their own right. The assessment characterized the major habitat features that may operate as controls or limiting factors on biotic assemblage composition under natural or anthropogenically disturbed circumstances. Within sample reaches, the field approach employed a randomized, systematic design, locating habitat observations on reaches with lengths 40 times their low flow wetted width. Two-person crews typically completed NWSA habitat measurements in 1.5 to 3.5 hours of field time. The resultant field measurements quantified major dimensions of channel morphology and stream habitat, allowing calculation of measures or indices of stream size and gradient, substrate size and stability, habitat complexity and cover, riparian vegetation cover and structure, anthropogenic disturbances, and channel-riparian interaction. We reduce the complexity of the raw field data by calculating metrics to summarize stream reach habitat characteristics. Beyond simple descriptions, the national assessment evaluated habitat indicators that reflect channel responses to basin-riparian disturbances, or elicit biotic when altered. In large regions, human land use disturbances typically overlay wide ranges of natural geomorphic factors that control both habitat characteristics and biotic assemblages. We discuss a variety of approaches for estimating the degree to which streams deviate from “natural” or “reference” conditions, including use of historical information, best professional judgment, reference sites, impairment criteria, and the use of process-based or empirical models to estimate reference condition. The survey produced descriptions of habitat adequate for regional assessments of habitat condition, establishing benchmarks for assessing future change, assessing likely causes of habitat alteration, and therefore evaluating relative risk for biotic impairment.